1. Technical Field
The invention relates to electronic communications networks. More particularly, the invention relates to a high speed physical layer for CSMA/CD systems.
2. Description of the Prior Art
In recent years, a number of technologies have been developed to solve customer needs for higher bandwidth networking. Of these technologies, several approaches have been developed in the IEEE's 802.3u committee to meet various customer wiring installations. While these technologies have their particular capabilities, each has its own specific shortcomings as well.
For example, 100BASE-TX technology offers full duplex operation at 125 MHz, yet it only requires two pair of cables when it is used on category 5 UTP or shielded twisted pair (STP). Further, 100BASE-TX is widely supported by industry. Unfortunately, this technology provides only marginal signal quality on poor to moderate CAT5 data grade unshielded twisted pair cable (UTP). See the ISO/IEC1801 Wiring Specification. 100BASE-TX is very difficult to Implement because of Its high bandwidth requirements. Thus, although this technology may be implemented with two pair of cables, in fact it requires all four pair of an unshielded twisted pair cable to ease noise sensitivities. Further, interoperability is difficult to achieve because of the small signal margin available, e.g. 1 volt peak amplitude during transmit. Because this technology is implemented using a continuous carrier technique that requires carrier coding, it is sensitive to noise, e.g. a single bit error can lead to the false detection of carrier sense. Finally, it should be noted that continuous carrier requires high power during ambient operation. This makes 100BASE-TX technology unattractive for low power or portable applications, such as for use with laptop computers.
100BASE-T4 technology supports CAT 3, 4, and 5 UTP cable. However, this technology only operates at half duplex, which limits its application for switched environments. At this time, there is no significant industry support for this technology because, for example, the complex waveshaping required to implement this technology has made interoperability difficult to achieve. Finally, performance of this technology is only marginal on CAT3 wire.
100BASE-T2 supports CAT 3, 4, and 5 UTP cables. Further, this technology provides full duplex operation. However, complex signalling requirements of this technology mandates the use of a digital signal processor (DSP). At this time, there is no known industry support for this technology. Finally, it should be noted that this technology is implemented with a continuous carrier that requires high power during ambient operation. This makes 100BASE-T2 technology unattractive for low power or portable applications, such as for use with laptop computers.
As can be seen from the above discussion, each of the existing technologies has substantial limitations. None of the 100BASE-TX alternatives share any common coding logic with 100BASE-TX and, therefore, there is no benefit to creating a multi-technology PHY using 100BASE-TX as the common base technology.
It would be advantageous to provide an electronic communications network technology that offered full duplex operation and robust performance on marginal CAT5 wiring, while taking advantage of industry standard 100BASE-TX functionality. It would be particularly advantageous if such technology were complementary to 100BASE-TX, as well as compatible with such 100BASE-T features as auto-negotiation.